Instructions, notices, and forms give printed information to the operator, often in connection with a product. It is of the utmost importance that this information is presented clearly and concisely and that it is easily read. This is particularly the case when an operator is faced with a new product, one that he rarely uses, or in a situation where time is limited.
The following rules apply:
1. Letters—Capitals alone are recommended for general use, but a combination of capitals and lowercase (small) letters are allowed (first letter a capital followed by lowercase letters). The ratio between width and height of the uprights should be between 1:6 and 1:8. The ratio of width to height of letters should be 3:5.
2. Short messages—In order to save time and space, the text should be as short as possible, whilst still retaining clarity.
3. Choice of words—Words and meanings should be kept as simple as possible (see above). Only well-known words should be used. For special populations of people, one may use common technical terms, for example, the use of aeronautical terms when addressing pilots.
4. Clarity—Instructions must be short and easily understood. One very simple way to test this is to try out different instructions on different people.
5. Contrast—In work where dark vision is required, letters should be white or light yellow on a black or other dark (e. g., brown) background. Where no dark vision is required, the letters should be black on a matt white background. Other colours may also be used for coding purposes, but they should always be chosen with maximum contrast in mind.
6. Size—The recommended size of letters depends on the reading distance. At a distance of 70 cm or less, in low lighting conditions, the size should be about 5 mm. In good light this can be reduced to 2.5 mm.